1. Field of the Invention
The present invention relates to an optical recording medium and, more particularly, to an arrangement of data stored on optical media that provides increased data reliability.
2. Discussion of the Related Art
Optical disks, which in general are disks that accept and retain information in the form of marks in a recording layer that can be read by an optical beam, are in wide use for high-density recording of digital information. Optical disks, for example, are used as compact disks (CDs), memory for computers, i.e., CD-ROMs, and DVDs. Conventionally, optical disks have a form factor that is greater than 50 mm and, in fact, the inside data track of conventional optical disks is larger than 50 mm.
Because dust or debris on the surface of the optical disk can obscure the data located on the recording layer beneath the dust or debris, data stored on an optical disk is stored with redundancy information that is used to assist in reading the data correctly in the presence of errors in the readback signal. The data bytes and the redundancy bytes that are associated with the data are organized as units known as codewords. Conventionally, codewords are organized into a two dimensional array, known as product codes. All the bytes of the array are assigned to two different codewords, a vertical (column) codeword and a horizontal (row) codeword. The codewords are generated using Reed-Solomon Error Correction Codes (RS ECC codes). In DVD data format, the data is conventionally arranged as a two dimensional array of 192 rows by 172 columns. With the addition of the redundancy bytes, the array becomes 208 rows by 182 columns. The row codeword is described as RS(182,172,11) denoting that there are 10 byes of redundancy per row. The column codeword is described as RS(208,192,17) denoting that there are 16 bytes of redundancy per column. For more information regarding ECC in general, see ECMA Standard-279, pp.25-30, December 1998, which is incorporated herein by reference.
The bytes of each column codeword are typically interleaved, i.e., arranged at intervals on the optical disk. Interleaving disperses data and the redundancy information over a large area. Consequently, the ability to correct continuous large errors, i.e., burst errors, is increased.
Conventional ECC blocks provide adequate data reliability with conventional optical disks, e.g., disk having a form factor greater than 50 mm. However, with a small form factor optical disk, a conventional ECC block does not provide adequate data reliability for small form factor optical disks.